WW2 ZigZag tracks

[spearfish]

I am reading a book about a wartime t-boat and the captain often sets different zigzag patterns to avoid being detected.Would any of you point me in the right direction of what these tracks looked like.The book was written in 1954 so i suppose they were still using them at the time hence the lack of detail.

 

[function]

In the surface world, basically they were and still are a way of countering the ASW threat, evasive steering was/is used to "deny the enemy submarine a valid fire control solution".
There were different plans for different scenarios, taking into account different conditions, convoys fast or slow, just warships on their own, the overall speed required to make the destination etc.
A base course would be signalled with a time check, then an 'in force plan' would be signalled, all ships having a copy of the relevant publication, this plan would then tell the convoy at what time past the hour to steer a course 'off' the base course, for example if they were steering 270, the first zigzag course would be 15 degrees to port then say 20 minutes later it would order them to steer 23 degrees to starboard and so on, the idea being that they would 'zig zag' along the base course, some plans had course changes every 2 to 3 minutes others 30 minute interval for example.
I don't know if this is what is meant in your book, I'd imagine it'll be something similar so they can escape detection and attack.


http://www.history.navy.mil/library/online/warinst-7.htm

 

[SailbadTheSinner]

ZigZags aren't to avoid detection - as any sundodger will tell you they can detect surface ships from extended distances

The purpose is to try and conceal the base course (preventing SMs from getting ahead - OK for SSKs but doesn't work for SSNs!) and also to add some unpredictability and hopefully spoil the firing solution (worked in the days of straight running torpedoes)

They still have a place but they are of limited value against SSNs and guided weapons

 

[andym]

Either that or the Nav Officer is having a fit!

 

[spearfish]

Thank all of you for your replies.The book describes events in the far east in 1944/5 in a t-boat.I don't think SSK had been invented then.The author Cmdr A.Mars gives the zigzags a letter,eg. Alpha etc.and uses this procedure to avoid detection.How many different patterns were there and what were the differences?

 

[wingnuts]

Several Types - different purposes:
VLLZZ very Long leg Zig Zags - strategic 12-24 hour changes - to disguise the overall desination of a force.
LLZZ- Long Leg Zig Zags - strategic 8-12 hour changes (could be on top of VLLZZ) - to make intellegence for submarine dificult and prevent it getting into the grain (i.e about 60 miles ahead of the general line of advance of the force)
SLZZ- short leg ZZ - to force submarine to sprint/snort/use radar to get into possible firing position if it was already in the grain.
Anto Torpedo ZZ a very SLZZ of 12-3 min legs to disrupt the SM firing solution
NB. Sensible skimmers never steered course of 5 or 10's of degrees cos the boat skipper knoew his sine rule in 5-10's of degres and maybe just maybe it would help.
The whole thing was boiled down in an Allied Tactical Publication post war. VLLZZ had numbers, LLZZ had letters and SLZZ had numbers, VSLZZ were either Z or Y and executed by a time - when you picked up the table of offsets from the SLZZ or LLZZ.
All this reduced the mean speed of Advance - hence you planned your force movememnts at about 8 knots - but ships doing a Anti Torpedo ZZ on top of a SLZZ ontop of a LLZZ etc where doing about 18knts (or just less tham cavitation inception speed) when the SM was about to fire!
Unles you wos the Belgrano - whose LLZZ had her pointing away from the falklands st the time of sinking - but her mean line of advance over the previous 24 hours was towards the falklands.

 

[spearfish]

Wingnut thankyou for the info.I dont suppose you could pm them to me in graphic form as a picture is always worth a thousand words?